US3544525A - Process for crystallization,drying and solid-state polymerization of polyesters - Google Patents
Process for crystallization,drying and solid-state polymerization of polyesters Download PDFInfo
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- US3544525A US3544525A US716089A US3544525DA US3544525A US 3544525 A US3544525 A US 3544525A US 716089 A US716089 A US 716089A US 3544525D A US3544525D A US 3544525DA US 3544525 A US3544525 A US 3544525A
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- pellets
- polyester
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- temperature
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- 229920000728 polyester Polymers 0.000 title description 55
- 238000002425 crystallisation Methods 0.000 title description 31
- 230000008025 crystallization Effects 0.000 title description 31
- 238000000034 method Methods 0.000 title description 28
- 230000008569 process Effects 0.000 title description 23
- 238000001035 drying Methods 0.000 title description 21
- 238000006116 polymerization reaction Methods 0.000 title description 16
- 239000008188 pellet Substances 0.000 description 64
- 239000007789 gas Substances 0.000 description 42
- 229920000642 polymer Polymers 0.000 description 30
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 15
- 238000001125 extrusion Methods 0.000 description 10
- 239000011261 inert gas Substances 0.000 description 9
- 238000010791 quenching Methods 0.000 description 9
- 238000005243 fluidization Methods 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 8
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 7
- 238000005520 cutting process Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 239000007788 liquid Substances 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- -1 polyethylene terephthalate Polymers 0.000 description 6
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- 238000009987 spinning Methods 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 230000015556 catabolic process Effects 0.000 description 4
- 230000007547 defect Effects 0.000 description 4
- 238000006731 degradation reaction Methods 0.000 description 4
- 239000000835 fiber Substances 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 229920000139 polyethylene terephthalate Polymers 0.000 description 4
- 239000005020 polyethylene terephthalate Substances 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 230000000717 retained effect Effects 0.000 description 4
- 238000003860 storage Methods 0.000 description 4
- 238000012546 transfer Methods 0.000 description 4
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 239000000428 dust Substances 0.000 description 3
- 238000000227 grinding Methods 0.000 description 3
- KKEYFWRCBNTPAC-UHFFFAOYSA-N Terephthalic acid Chemical compound OC(=O)C1=CC=C(C(O)=O)C=C1 KKEYFWRCBNTPAC-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 239000004305 biphenyl Substances 0.000 description 2
- 235000010290 biphenyl Nutrition 0.000 description 2
- 125000006267 biphenyl group Chemical group 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 229920001577 copolymer Polymers 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000009477 glass transition Effects 0.000 description 2
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000005453 pelletization Methods 0.000 description 2
- ZUOUZKKEUPVFJK-UHFFFAOYSA-N phenylbenzene Natural products C1=CC=CC=C1C1=CC=CC=C1 ZUOUZKKEUPVFJK-UHFFFAOYSA-N 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- 230000003134 recirculating effect Effects 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- GRYSXUXXBDSYRT-WOUKDFQISA-N (2r,3r,4r,5r)-2-(hydroxymethyl)-4-methoxy-5-[6-(methylamino)purin-9-yl]oxolan-3-ol Chemical compound C1=NC=2C(NC)=NC=NC=2N1[C@@H]1O[C@H](CO)[C@@H](O)[C@H]1OC GRYSXUXXBDSYRT-WOUKDFQISA-N 0.000 description 1
- BSZXAFXFTLXUFV-UHFFFAOYSA-N 1-phenylethylbenzene Chemical compound C=1C=CC=CC=1C(C)C1=CC=CC=C1 BSZXAFXFTLXUFV-UHFFFAOYSA-N 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- OFOBLEOULBTSOW-UHFFFAOYSA-N Malonic acid Chemical compound OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 description 1
- UFWIBTONFRDIAS-UHFFFAOYSA-N Naphthalene Chemical compound C1=CC=CC2=CC=CC=C21 UFWIBTONFRDIAS-UHFFFAOYSA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 238000005267 amalgamation Methods 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- VEIOBOXBGYWJIT-UHFFFAOYSA-N cyclohexane;methanol Chemical compound OC.OC.C1CCCCC1 VEIOBOXBGYWJIT-UHFFFAOYSA-N 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000002939 deleterious effect Effects 0.000 description 1
- 238000001739 density measurement Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000010981 drying operation Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000010525 oxidative degradation reaction Methods 0.000 description 1
- 239000002685 polymerization catalyst Substances 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 230000008439 repair process Effects 0.000 description 1
- 230000003252 repetitive effect Effects 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 239000004753 textile Substances 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/12—Powdering or granulating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B13/00—Conditioning or physical treatment of the material to be shaped
- B29B13/06—Conditioning or physical treatment of the material to be shaped by drying
- B29B13/065—Conditioning or physical treatment of the material to be shaped by drying of powder or pellets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/02—Making granules by dividing preformed material
- B29B9/06—Making granules by dividing preformed material in the form of filamentary material, e.g. combined with extrusion
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/02—Making granules by dividing preformed material
- B29B9/06—Making granules by dividing preformed material in the form of filamentary material, e.g. combined with extrusion
- B29B9/065—Making granules by dividing preformed material in the form of filamentary material, e.g. combined with extrusion under-water, e.g. underwater pelletizers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/16—Auxiliary treatment of granules
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/78—Preparation processes
- C08G63/80—Solid-state polycondensation
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/88—Post-polymerisation treatment
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B5/00—Drying solid materials or objects by processes not involving the application of heat
- F26B5/08—Drying solid materials or objects by processes not involving the application of heat by centrifugal treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/16—Auxiliary treatment of granules
- B29B2009/165—Crystallizing granules
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
Definitions
- Polyesters with a crystallization temperature at least 50 C. above their glass transition temperature are prepared in a continuous operation by contacting the molten polyester with a liquid such as water for a period of time sufficient to facilitate converting the polyester extrud-ate into pellets.
- the pellets are immediately removed from contact with the liquid or quenching medium before an equilibrium temperature is established in the pellets so that the maximum amount of heat possible is retained which reduces substantially the residence time in the crystallization chamber prior to entering a solid-state polymerization and/or drying tower directly fromthe crystallization chamber.
- the total time required to quench, pelletize, de-water and transfer the polyester pellets to a fluidized crystallization chamber is less than six seconds. Crystallization occurs in a few minutes in the fluidized zone and the crystallized pellets are passed directly to the drying and polymerization tower wherein solid-state polymerization is accomplished, if desired, under plug flow conditions utilizing a gas moving countercurrent to the polyester.
- the gas is heated to about 180-210 C. and moved at a superficial velocity of 0.5 to 2.0 ft./sec. for a period of time sufiicient to achieve the desired molecular weight.
- the particulate polyester must be crystallized at a temperature below its stick point temperature to avoid amalgamation of the polyester pellets into a solid and intractable mass.
- Several different types of processes for crystallizing polyester pellets are well known.
- the batch-type processes such as disclosed in US. Pat. No. 3,104,011 utilize means for treating the polyester pellets with mediums such as steam, toluene and water elevated to temperatures above 100 C. to achieve crystallization in a batch operation.
- the stick point temperature of a crystallized polyester is 230-240 C. However, prior to crystallization it may stick at temperatures above about 70 C.
- the continuous processes employed heretofore generally involve massive equipment in relation to the quantity of polyester pellets dried. These methods utilize relatively long periods of crystallization, usually more than two hours. This is attributed to the failure of the practitioners to recognize the unexpected results which may be obtained if the polyester extrudate is contacted only briefly with a quench medium so as not to remove heat from the surface of the pellets other than as required to facilit-ate cutting into oblong or pillow-shaped pellets.
- a further improvement in the technology for producing polyesters is represented by solid-state polymerization processes such as described in British Pat. No. 1,004,462 wherein solid-state polymerization is accomplished by grinding the particulate polyester to form a fine powder which is charged into a powder build-up reactor where it is vacuum purged to remove oxygen and heated in the presence of a polymerization catalyst while reducing the pressure to obtain the desired molecular weight.
- the problem encountered with these processes is the economic disadvantage imposed by the grinding operation and difficulty in obtaining uniform particle size.
- the large surface area available in powdered or ground polyester presents a substantially greater surface area to oxidation which results in a significant increase in breaks, wraps, and other defects when the polymer is spun or drawn into yarn.
- the process of the present invention involves the rapid crystallization, drying and/or solid-state polymerization of polyesters for use primarily in the production of textile fibers.
- the process comprises the extrusion of a molten polymer through an extrusion die having multiple orifices. As the extrudate emerges from the orifices it is contacted with a liquid at 15-70 C. having a heat capacity of at least 0.6 cal./gram/ C. for about 0.01 to about 3 seconds to merely chill or solidify the skin or surface layers sufiiciently to facilitate cutting the extrudate into pellets.
- the pellets are transferred immediately from contact with the liquid to a fluidized zone maintained at about -190 C., preferably l80 (3., wherein the discrete particles are circulated for approximately 2 minutes with a hot gas having a superficial velocity of at least 2.3 ft./sec.
- a hot gas having a superficial velocity of at least 2.3 ft./sec.
- the temperature in this vessel is maintained at about 3 210 C. by passing a hot gas through the polyester pellets until the desired moisture level and/or molecular weight level is reached.
- Superficial velocity is defined as the gas velocity calculated on the basis that the vessel is free of polymer.
- Entrainment ofthe polyester particles in the heated gas to produce a fluidized bed is carried out in a vertical ves sel' having the inlets and outlets for introducing and removing the constituents properly disposed to achieve an eflicient operation.
- the particles are entrained in a fluid medium such as air and introduced into the vessel into the hot gas being circulated therein.
- polyesters which may be employed with this invention are substantially linear fiber-forming polyesters hav-' ing recurring cyclic structure in the polymer backbone with an intrinsic viscosity in phenolztetrachlorethane 60:40 weight ratio of from about 0.5 to 1.3 deciliters per gram. Viscosity is determined at 25 C. with solutions of the polymer in phenolztetrachlorethane containing 0.5 gram of polymer per 100 milliliters of phenolztetrachlorethane.
- the preferred polyester is polyethylene terephthalate although others may be employed, particularly those in which one component of the recurring unit in the polyester chain is derived from terephthalic acid, diphenyl methanep,p'dicarboxylic acid, diphenyl p-pdicarboxylic acid, diphenyl ethane p,pdicarboxylic acid, or napthalene dicarboxylic acids such as napthalene 2,6- and napthalene- 2,7-dicarboxylic acids.
- molten polyester is supplied from a reactor vessel 1 via discharge from a screw pump, not shown, to a molten polymerpump 2 and is discharged through line 3 to an underwater pelletizer 4 which'is of conventional design.
- Pressure developed by the polymer pump 2 which is in the region of 1,000 to 2,000 p.s.i.g., forces the melt out of an extrusion die 5 containing multiple orifices having diameters generally from about 0.10 to 0.15 inch.
- extrusion dies having about 270 orifices are employed for an extrusion rate of about 2,000 to 4,000 pounds of polymer melt per hour.
- the orifices are spaced regularly around a four-inch diameter die plate. As the melt emerges from the face of the die plate, a knife positioned adjacent to the plate is rotated by motor 4a to sever the individually formed streams into pellets. A chamber 15a is formed between the housing of the underwater pelletizer 4 and the extrusion die 5.
- a quench medium such as water is introduced into chamber 15a to contact and solidify the emerging extrudate.
- Water having a specific heat capacity of about 1.0 cal./ gram is supplied at a rate of approximately 100 gallons per minute and a velocity of at least 2.5 ft./ sec. axial to the die plate 5 by recirculating pump 35.
- the temperature of the water Prior to entering the chamber 1512 the temperature of the water is adjusted to about 42 C. by a heat exchanger 34. After the pellets become entrained in the flow of water, both exit chamber 15a through line 7 at a water temperature of about 55 C. Since the temperature rise is greater than the amount of heat loss from the polyester pellets, it is expected that the excess heat is gained from the heated die plate.
- the pressures, flow rates and speed of cutting blades are regulated to produce a pellet of between about 0.06 to 0.15 inch which is characterized by a length not greater than 1.5 times its diameter and not less than 0.6 times its diameter.
- a pellet of between about 0.06 to 0.15 inch which is characterized by a length not greater than 1.5 times its diameter and not less than 0.6 times its diameter.
- percent of the pellets retained on a No. 8 U.S. screen and even more preferably, about percent retained on a N0. 8 U.S. screen.
- water temperatures are higher than 70 C., there is a tendency for the pellets to fuse together and produce a nonuniform particle size for future operations. Additionally, at too high a temperature, there are elongated polymer tails and sheets or strings which result in an increase in the final product defects.
- the velocity of water in chamber 15 is greater than 2.5 ft./ sec. in the region of die plate.
- the molten polymer from pump 2 passes along line 43 and exits from extrusion die 44 as a series of strands and passes through a water bath 63 for a short distance then passes between upper and lower blow discs 56, 54 which may employ heated air to remove surface moisture.
- the strands then enter pelletizer 62 where polymer pellets of 0.06 to 0.15 inch diameter by 0.08 to 0.20 inch in length are cut. These pellets pass via line 53 into. dewaterer 9. Chilled water entersthrough valve 49 and passes through heat exchanger 52 and overflows at 48. The water may be recirculated to heat exchanger 52 via a pumping system, not shown.
- Centrifugal dewatering is accomplished by discharging the water at exit 11 in the bottom of the dewatering unit 9 and separating the pellets from the liquid bath through the rotation of a fan which is driven by motor 10.
- the pellets leave the dewatering unit at exit 12 and enter into a fluidizing column 15 through inlet 14 located approximately one-third the height of the vessel 16 from the top thereof.
- a gas flow is introduced into inlet 14 via line 13 from a source not shown to aid in the transfer of the pellets from the dewatering unit 9 to the fluidized zone.
- the heated gas enters through a plenum chamber 25 and exits through return line 23.
- the pellets become under the influence of the entering hot gas which establishes a fluidization flow of the pellets up the center of the vessel and down the sides until eventually after repetitive recirculations the pellets become crystallized and a portion of the recirculating quantity overflows into a central discharge 6 and exits through a rotary discharge means 36.
- a specific residence time during which polymer pellets are admixed with already crystallized pellets in column 15, and the pellets circulate past the pipe in the center of the column until eventual overflow occurs.
- the gas employed for establishing the fluidizing column 15 of pellets has a dew point of less than 15 C. Moisture in the gas accelerates the crystallization.
- an inert gas such as nitrogen or carbon dioxide is used during crystallization.
- the gas is circulated in through a closed system with make-up gas being introduced as necessary through valve 27.
- the gas is passed through a dryer bed 28, 29 upstream from a gas circulation blower 30 which forces the dried gas through a heat exchanger 31.
- the heated gas is passed through a candle filter 26' of at least /2 inch thickness and having a porosity of 1 to 2 microns. After being filtered, the gas enters the fluidization column 16 at 37 and/ or at valve 33. Recirculation gas is used after passing through filter 38. A portion of the heated gas may bypass the fluidization column for purposes to be described later herein.
- the deoxygenator 32 is employed when an inert gas is used to avoid build up of oxygen which can occur with continuous recirculation. The deoxygenator 32 maintains oxygen below 50 parts per million and preferably below parts per million.
- the superficial velocity of the gas entering at is greater than 2.3 ft./sec., preferably about 3.2 ft./ sec. within the column 15, to keep the entire column in fluidized circulation.
- the fluidized gas having having oligomers and dust entrained therewith exits at 17 and impinges against a vertical pipeline 23 whereby the solids fall down toward valve 18.
- the drain line 19 is purged by a vacuum line 21 and the inert gas line 22. Traces of violatile ethylene glycol and other very low molecular weight materials move through line 23 to a condenser 60 and then to storage tank 61 where they can be sent to the recovery process. It is important that polymer dust and skins be removed since these unwanted constituents produce many defects.
- the polymer moisture is between 0.05 and 0.2 percent as it passes from the dewaterer at exit 12. Consequently, very little moisture must be removed from the polymer in subsequent drying operations.
- the low moisture content is attributed to the fact that the contact time between the extruded polyester and the quench medium is so short that only the skin layers are penetrated. For example, the total time required for extruding, cutting and dewatering the polyester pellets in accordance with the present invention is less than six seconds.
- the temperature of the gas chamber 15 through plenum chamber 25 is controlled between about 130 and 190 (3., but preferably about 150-180 C. since the maximum safe crystallization temperature occurs at this point for polyethylene terephthalate.
- crystallization can be accomplished in a matter of minutes by the procedures of this invention as contrasted by hours with the prior art processes.
- the rapid crystallization achieved by the process of this invention is due to the maximum amount of heat retained in the polyester pellets at the time of entering the fluidized zone where crystallization occurs. For maximum crystallization rates it has been found that the temperature and contact time between the quench medium and the polyester should be controlled to the extent that the average temperature of the pellets does not drop below C.
- Crystallization rates are related quite significantly to the temperature.
- Table I illustrates the time required to achieve 60 percent crystallization of polyester pellets having an average temperature of about 130 C. when subjected to fluidized gas ranging in elevated temperatures of 130-200 C.
- the preferred temperature conditions for optimized crystallization are between and 190 C. At either higher or lower temperatures, a significant increase in time occurs. Furthermore, when the crystallization temperatures exceed 190 C., there is a tendency for the pellets to fuse together during the crystallization process even though agitated continuously.
- the data of Table I has been plotted graphically in FIG. 2 to better illustrate these results.
- a receiver unit 40 is provided for storage to accommodate reloading of the crystallizer column 15, or for changeover in product or equipment repairs.
- the pellets may be dried further to remove moisture and glycol, or an increase in molecular weight may be effected through solid-state polymerization, depending upon the temperature of the heated gas and its volume. In the event solidstate polymerization is carried out it is desirable that an inert gas such as nitrogen or carbon dioxide be used.
- burner gas which is about 85 percent nitrogen, 12 percent CO and 1-2 percent hydrogen and small amounts of methane and carbon monoxide, is employed to prevent oxidative degradation of the polymer. Degradation becomes apparent from a higher percentage of breaks and wraps in filaments spun therefrom.
- the drying medium whether an inert gas or air, is delivered through line 42 by blower 30 to a heater 43 where it is heated to a temperature between and 212 C. prior to entering the bottom section 45 of the tower 47 through a plenum chamber 46.
- the gas velocity in tower 47 is below fiuidization rates and therefore the gas moves upward through the mass of polyester pellets at a superficial velocity of below 2.1 ft./ sec.
- the gas is exhausted through plenum chamber 51 into a gas return line which is connected to a volatile recovery sys tern, 60, 61. Subsequent to removal of glycol and oligomers in condenser 60 and storage tank 61, the gas is returned to the gas recirculation system.
- a level controller 50 is positioned near the top of tower 47 for controlling the residence time of the polymer within the tower.
- the discharge rotary valve 58 is actuated by the level control mechanism to release the material at the same rate of introduction.
- a receiver 51 is The polymer lots that were processed by solid-state polymerization in accordance with the present invention exhibited a significant drop in breaks and wraps when spun into fibers. Approximately 50 percent less breaks and wraps were encountered.
- the improved properties are beprovided to function as a surge means on the continuous lieved to be attributed to the removal of low molecular y f 111 cases of Product ug overs or equlpmentreweight material from the polyester. Therefore, the forepalr.
- the polymer after having attalned the deslred going improvements make the products of this invention molecular weight and/or purity 1s forwarded to a blender particularly de irable for the production of fibers h re 55 where the pellets undergo a. thorough blending prior spin-draw te hni ue are used, to being forwarded to spinning y t s
- the height and diameter of the crysa more e e dlsclosvre of the dry1ng app tallizer, in feet was 33/3, 33/3, 40/4 and 40/4, respectivep y hereln Wlth regard to opefatlng eendltlons See 1y.
- the molecular weight increase is illustrated graphically in FIG. 3 as a function of temperature by plotting the rate of molecular weight increase per hour against the temperature at a constant gas flow of 2.0 ft./sec. superrficial velocity. It will be noticed that the rate of increase is quite rapid for temperatures beginning at 180 C. and continues to increase until reaching 210 C. at which point the rate decreases rapidly. It may also be noticed that in the absence of sufficient inert gas flow or equivalent partial pressure reducing technique that essentially no rise in molecular weight occurs.
- the cross-sectional area of the drying column employed was 2.8 times greater than the crystallizer column for Examples 7 and 8 and 6.3 times greater for Examples 9 and 10.
- a crystallizer having a cross-sectional area of less than 2.0 the manufacturing costs and mechanical problems make these operations unsatisfactory.
Description
Dec. 1, 1970 J BAUNT ETAL 3,544,525
PROCESS FOR CRYST LLIZATION. DRYING AND SOLID-STATE POLYMERIZATION OF POLYESTERS Filed March 26, 1968 2 Sheets-Sheet l TO STORAGE OR SPINNING o m 1- g m m p. u v v In| (D LO INVENTORS:
LASZLO JOSEPH BALINT RAMON LUIS ABOS ORVILL EDWARD SNIDER ATTORNEY Dec. 1, 1970 L. J. BALINT ETAL 3,544,525 PROCESS FOR CRYSTALLIZATION, DRYING AND SOLID-STATE POLYMERIZATION OF POLYESTERS 2 Sheets-Sheet 2 Filed March 26, 1968 90% CRYSTALLINITY 80% CRYSTALLINITY 70% CRYSTALLINITY I 60% CRYSTALLINITY 50% CRYSTALLINITY mmtbzi 2 m2; wozw mmm I60 I80 TEMPERATURE C mac: 51 m 5ow o2 Es:
I80 I90 TEMPERATURE C T R E m D m m 35 0 TM EAA D JWE RON.L 0 L zoll AAR VLRO m United States Patent US. Cl. 260-75 8 Claims ABSTRACT OF THE DISCLOSURE Polyesters with a crystallization temperature at least 50 C. above their glass transition temperature are prepared in a continuous operation by contacting the molten polyester with a liquid such as water for a period of time sufficient to facilitate converting the polyester extrud-ate into pellets. The pellets are immediately removed from contact with the liquid or quenching medium before an equilibrium temperature is established in the pellets so that the maximum amount of heat possible is retained which reduces substantially the residence time in the crystallization chamber prior to entering a solid-state polymerization and/or drying tower directly fromthe crystallization chamber. The total time required to quench, pelletize, de-water and transfer the polyester pellets to a fluidized crystallization chamber is less than six seconds. Crystallization occurs in a few minutes in the fluidized zone and the crystallized pellets are passed directly to the drying and polymerization tower wherein solid-state polymerization is accomplished, if desired, under plug flow conditions utilizing a gas moving countercurrent to the polyester. The gas is heated to about 180-210 C. and moved at a superficial velocity of 0.5 to 2.0 ft./sec. for a period of time sufiicient to achieve the desired molecular weight.
BACKGROUND OF THE INVENTION The production of crystallized polyesters in particulate form heretofore has involved relatively massive and complex fluidization procedures. The processes employed have required large initial investments for equipment cost and have been expensive to operate. These disadvantages are caused at least in part by the relatively long crystallization cycles that are employed in the prior art processes. Another disadvantage resulting from the long crystallization periods is the deleterious effects of oxygen.
The particulate polyester must be crystallized at a temperature below its stick point temperature to avoid amalgamation of the polyester pellets into a solid and intractable mass. Several different types of processes for crystallizing polyester pellets are well known. The batch-type processes such as disclosed in US. Pat. No. 3,104,011 utilize means for treating the polyester pellets with mediums such as steam, toluene and water elevated to temperatures above 100 C. to achieve crystallization in a batch operation. The stick point temperature of a crystallized polyester is 230-240 C. However, prior to crystallization it may stick at temperatures above about 70 C.
While such processes represent an advancement over some earlier methods, they have certain undesired limitations. The prolonged crystallization times generally required in conjunction with the batch operation are not desirable for economic production of polyesters, especially for end uses which require polymers having very low moisture content. Such technology requires a considerable expenditure in utilities and time to reheat the polyester pellets to the desired temperature. Also, an occasional ice failure of a control mechanism results in the pellets setting up in an intractable mass.
The continuous processes employed heretofore generally involve massive equipment in relation to the quantity of polyester pellets dried. These methods utilize relatively long periods of crystallization, usually more than two hours. This is attributed to the failure of the practitioners to recognize the unexpected results which may be obtained if the polyester extrudate is contacted only briefly with a quench medium so as not to remove heat from the surface of the pellets other than as required to facilit-ate cutting into oblong or pillow-shaped pellets.
A further improvement in the technology for producing polyesters is represented by solid-state polymerization processes such as described in British Pat. No. 1,004,462 wherein solid-state polymerization is accomplished by grinding the particulate polyester to form a fine powder which is charged into a powder build-up reactor where it is vacuum purged to remove oxygen and heated in the presence of a polymerization catalyst while reducing the pressure to obtain the desired molecular weight. The problem encountered with these processes is the economic disadvantage imposed by the grinding operation and difficulty in obtaining uniform particle size. The large surface area available in powdered or ground polyester presents a substantially greater surface area to oxidation which results in a significant increase in breaks, wraps, and other defects when the polymer is spun or drawn into yarn. These defects are particularly troublesome in the production of polymer spinning systems that are diflicult to control such as blends of polymers. Furthermore, as in the other processes discussed herein'above, conventional quenching times and temperatures are employed whereby the particulate polyester is cooled to a temperature level low enough to permit grinding thereof.
In the production of the high molecular weight polyester for industrial end uses, mechanical difiiculties are encountered in moving, stripping and purifying these products due to the high melt viscosity. The achievement of the high melt viscosity is realized through the maintenance of the molten polyester at prolonged residence times at high temperatures whereby product degradation occurs resulting in poor spun yarn properties characterized by an increase in breaks, wraps, drips and other spinning difliculties as a result of the oxidation and/or general degradation of the polymers.
With the foregoing discussion in mind, the provision of a process which reduces substantially the production costs of polyesters that can be shaped in articles having improved properties would represent a substantial improvement in the art.
SUMMARY OF THE INVENTION The process of the present invention involves the rapid crystallization, drying and/or solid-state polymerization of polyesters for use primarily in the production of textile fibers. The process comprises the extrusion of a molten polymer through an extrusion die having multiple orifices. As the extrudate emerges from the orifices it is contacted with a liquid at 15-70 C. having a heat capacity of at least 0.6 cal./gram/ C. for about 0.01 to about 3 seconds to merely chill or solidify the skin or surface layers sufiiciently to facilitate cutting the extrudate into pellets. The pellets are transferred immediately from contact with the liquid to a fluidized zone maintained at about -190 C., preferably l80 (3., wherein the discrete particles are circulated for approximately 2 minutes with a hot gas having a superficial velocity of at least 2.3 ft./sec. As the pellets become crystallized, they are discharged from the fluidized zone and charged into a vessel for drying and/or solid-state polymerization. The temperature in this vessel is maintained at about 3 210 C. by passing a hot gas through the polyester pellets until the desired moisture level and/or molecular weight level is reached. Superficial velocity is defined as the gas velocity calculated on the basis that the vessel is free of polymer.
Entrainment ofthe polyester particles in the heated gas to produce a fluidized bed is carried out in a vertical ves sel' having the inlets and outlets for introducing and removing the constituents properly disposed to achieve an eflicient operation. Preferably, the particles are entrained in a fluid medium such as air and introduced into the vessel into the hot gas being circulated therein. Once the continuous operation is established, the incoming polyester is admixed with polyester pellets in the crystallizer vessel of which contains not more than 20 weight percent of noncrystallized polyester and the remaining 80 percent in said vessel having a crystallinity of at least 50 percent,
as determined by density measurements. It is essential that these conditions be closely observed. If a greater quantity of noncrystallized material is present or if the remaining portion of thepolyester possesses lessthan 50 percent crystallinity or if the zone of contact is not in mechanical motion equal to that obtainable in fluidized state or should the zone of feed of the noncrystallized material result in bypassing the crystallization zone, the polyester pellets will tend to stick together thereby forming an intractable mass which will plug outlet points in both the crystallization zone and within the drying column. Thus the sticky pellets cause severe mechanical difliculties which are obviously objectionable.
The polyesters which may be employed with this invention are substantially linear fiber-forming polyesters hav-' ing recurring cyclic structure in the polymer backbone with an intrinsic viscosity in phenolztetrachlorethane 60:40 weight ratio of from about 0.5 to 1.3 deciliters per gram. Viscosity is determined at 25 C. with solutions of the polymer in phenolztetrachlorethane containing 0.5 gram of polymer per 100 milliliters of phenolztetrachlorethane. The preferred polyester is polyethylene terephthalate although others may be employed, particularly those in which one component of the recurring unit in the polyester chain is derived from terephthalic acid, diphenyl methanep,p'dicarboxylic acid, diphenyl p-pdicarboxylic acid, diphenyl ethane p,pdicarboxylic acid, or napthalene dicarboxylic acids such as napthalene 2,6- and napthalene- 2,7-dicarboxylic acids.
Various aliphatic glycols, generally 2-4 carbons and the trans and cis isomers of 1-4 cyclohexane dimethanol may be reacted with the indicated diacids. Block and random' copolymers "of these materials may be employed. However, if a random nonisomorphic copolymer is used, not more than 30'percent of a second polymercan be present, otherwise, the crystallinity and softening point are reduced below a usable range.
BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings in detail and particularly FIG. 1, molten polyester is supplied from a reactor vessel 1 via discharge from a screw pump, not shown, to a molten polymerpump 2 and is discharged through line 3 to an underwater pelletizer 4 which'is of conventional design. Pressure developed by the polymer pump 2, which is in the region of 1,000 to 2,000 p.s.i.g., forces the melt out of an extrusion die 5 containing multiple orifices having diameters generally from about 0.10 to 0.15 inch. Usually extrusion dies having about 270 orifices are employed for an extrusion rate of about 2,000 to 4,000 pounds of polymer melt per hour. The orifices are spaced regularly around a four-inch diameter die plate. As the melt emerges from the face of the die plate, a knife positioned adjacent to the plate is rotated by motor 4a to sever the individually formed streams into pellets. A chamber 15a is formed between the housing of the underwater pelletizer 4 and the extrusion die 5.
In order to facilitate efficient cutting of the polymer streams into pellets, a quench medium such as water is introduced into chamber 15a to contact and solidify the emerging extrudate. Water having a specific heat capacity of about 1.0 cal./ gram is supplied at a rate of approximately 100 gallons per minute and a velocity of at least 2.5 ft./ sec. axial to the die plate 5 by recirculating pump 35. Prior to entering the chamber 1512 the temperature of the water is adjusted to about 42 C. by a heat exchanger 34. After the pellets become entrained in the flow of water, both exit chamber 15a through line 7 at a water temperature of about 55 C. Since the temperature rise is greater than the amount of heat loss from the polyester pellets, it is expected that the excess heat is gained from the heated die plate.
The pressures, flow rates and speed of cutting blades are regulated to produce a pellet of between about 0.06 to 0.15 inch which is characterized by a length not greater than 1.5 times its diameter and not less than 0.6 times its diameter. Typically, it is preferred to have percent of the pellets retained on a No. 8 U.S. screen and even more preferably, about percent retained on a N0. 8 U.S. screen. If water temperatures are higher than 70 C., there is a tendency for the pellets to fuse together and produce a nonuniform particle size for future operations. Additionally, at too high a temperature, there are elongated polymer tails and sheets or strings which result in an increase in the final product defects. 'At an inlet water temperature below 15 C., there is a tendency for pellets to freeze in the exit orifices of the die or become restricted at the exit thereof resulting in thin pellets and/ or plugging of the die outlet holes. Therefore, it is highly preferable to control the polymer melt temperatures at the extrusion die 5 as near as practical to its solidification point since this contributes to the firmness of the emerging extrudate and results in a firmer, more uniform cut by the pelletizing knife. Cutting performance is further influenced by the diameter size of the polymer being cut which is determined by hole size, viscosity and temperature of the particular polymer being extruded. After extrusion and cutting the pellets are transferred from the underwater pelletizer 4 to a dewater unit 9. The velocity of water in chamber 15 is greater than 2.5 ft./ sec. in the region of die plate. Alternately, the molten polymer from pump 2 passes along line 43 and exits from extrusion die 44 as a series of strands and passes through a water bath 63 for a short distance then passes between upper and lower blow discs 56, 54 which may employ heated air to remove surface moisture. The strands then enter pelletizer 62 where polymer pellets of 0.06 to 0.15 inch diameter by 0.08 to 0.20 inch in length are cut. These pellets pass via line 53 into. dewaterer 9. Chilled water entersthrough valve 49 and passes through heat exchanger 52 and overflows at 48. The water may be recirculated to heat exchanger 52 via a pumping system, not shown.
Centrifugal dewatering is accomplished by discharging the water at exit 11 in the bottom of the dewatering unit 9 and separating the pellets from the liquid bath through the rotation of a fan which is driven by motor 10. The pellets leave the dewatering unit at exit 12 and enter into a fluidizing column 15 through inlet 14 located approximately one-third the height of the vessel 16 from the top thereof. A gas flow is introduced into inlet 14 via line 13 from a source not shown to aid in the transfer of the pellets from the dewatering unit 9 to the fluidized zone. Once the pellets enter into vessel 15 they become entrained in a heated gas circulating within the confines of the vessel to establish a fluidized bed of the pellets. The heated gas enters through a plenum chamber 25 and exits through return line 23. The pellets become under the influence of the entering hot gas which establishes a fluidization flow of the pellets up the center of the vessel and down the sides until eventually after repetitive recirculations the pellets become crystallized and a portion of the recirculating quantity overflows into a central discharge 6 and exits through a rotary discharge means 36. Thus, there is a specific residence time during which polymer pellets are admixed with already crystallized pellets in column 15, and the pellets circulate past the pipe in the center of the column until eventual overflow occurs.
The gas employed for establishing the fluidizing column 15 of pellets has a dew point of less than 15 C. Moisture in the gas accelerates the crystallization. Preferably, an inert gas such as nitrogen or carbon dioxide is used during crystallization.
As shown in FIG. 1, the gas is circulated in through a closed system with make-up gas being introduced as necessary through valve 27. The gas is passed through a dryer bed 28, 29 upstream from a gas circulation blower 30 which forces the dried gas through a heat exchanger 31. The heated gas is passed through a candle filter 26' of at least /2 inch thickness and having a porosity of 1 to 2 microns. After being filtered, the gas enters the fluidization column 16 at 37 and/ or at valve 33. Recirculation gas is used after passing through filter 38. A portion of the heated gas may bypass the fluidization column for purposes to be described later herein. The deoxygenator 32 is employed when an inert gas is used to avoid build up of oxygen which can occur with continuous recirculation. The deoxygenator 32 maintains oxygen below 50 parts per million and preferably below parts per million.
The superficial velocity of the gas entering at is greater than 2.3 ft./sec., preferably about 3.2 ft./ sec. within the column 15, to keep the entire column in fluidized circulation. The fluidized gas having having oligomers and dust entrained therewith exits at 17 and impinges against a vertical pipeline 23 whereby the solids fall down toward valve 18. Thus, the entrained oligomers and dust that result from the fluidization motion are removed through line 19 at 20. The drain line 19 is purged by a vacuum line 21 and the inert gas line 22. Traces of violatile ethylene glycol and other very low molecular weight materials move through line 23 to a condenser 60 and then to storage tank 61 where they can be sent to the recovery process. It is important that polymer dust and skins be removed since these unwanted constituents produce many defects.
Generally, the polymer moisture is between 0.05 and 0.2 percent as it passes from the dewaterer at exit 12. Consequently, very little moisture must be removed from the polymer in subsequent drying operations. The low moisture content is attributed to the fact that the contact time between the extruded polyester and the quench medium is so short that only the skin layers are penetrated. For example, the total time required for extruding, cutting and dewatering the polyester pellets in accordance with the present invention is less than six seconds.
The temperature of the gas chamber 15 through plenum chamber 25 is controlled between about 130 and 190 (3., but preferably about 150-180 C. since the maximum safe crystallization temperature occurs at this point for polyethylene terephthalate. As stated earlier herein, crystallization can be accomplished in a matter of minutes by the procedures of this invention as contrasted by hours with the prior art processes. The rapid crystallization achieved by the process of this invention is due to the maximum amount of heat retained in the polyester pellets at the time of entering the fluidized zone where crystallization occurs. For maximum crystallization rates it has been found that the temperature and contact time between the quench medium and the polyester should be controlled to the extent that the average temperature of the pellets does not drop below C. Therefore, it is extremely important that the time required to transfer the pellets from the quenching zone to the fluidization zone be held to a minimum to avoid fusing of the pellets. Should the average temperature of the pellets drop substantially below 130 C., as is the conventional practice, a matter of hours is required in reheating and crystallizing the material.
The crystallization rates are related quite significantly to the temperature. Table I below illustrates the time required to achieve 60 percent crystallization of polyester pellets having an average temperature of about 130 C. when subjected to fluidized gas ranging in elevated temperatures of 130-200 C.
TABLE I Minutes to attain 60 percent crystallinity Temperature at fluidized gas, C.:
As can be seen from Table I, the preferred temperature conditions for optimized crystallization are between and 190 C. At either higher or lower temperatures, a significant increase in time occurs. Furthermore, when the crystallization temperatures exceed 190 C., there is a tendency for the pellets to fuse together during the crystallization process even though agitated continuously. The data of Table I has been plotted graphically in FIG. 2 to better illustrate these results.
When the particles become crystallized in column 15 they overflow through the center pipe 6 and exit at the rotary discharge means 36 for transfer through valve 39 into a drying or solid-state polymerization tower 47. A receiver unit 40 is provided for storage to accommodate reloading of the crystallizer column 15, or for changeover in product or equipment repairs. The pellets may be dried further to remove moisture and glycol, or an increase in molecular weight may be effected through solid-state polymerization, depending upon the temperature of the heated gas and its volume. In the event solidstate polymerization is carried out it is desirable that an inert gas such as nitrogen or carbon dioxide be used. Generally burner gas, which is about 85 percent nitrogen, 12 percent CO and 1-2 percent hydrogen and small amounts of methane and carbon monoxide, is employed to prevent oxidative degradation of the polymer. Degradation becomes apparent from a higher percentage of breaks and wraps in filaments spun therefrom.
The drying medium, whether an inert gas or air, is delivered through line 42 by blower 30 to a heater 43 where it is heated to a temperature between and 212 C. prior to entering the bottom section 45 of the tower 47 through a plenum chamber 46. At temperatures above 212 C. there is a tendency for polyester pellets to tackify and stick. The gas velocity in tower 47 is below fiuidization rates and therefore the gas moves upward through the mass of polyester pellets at a superficial velocity of below 2.1 ft./ sec. After passing through the drying column the gas is exhausted through plenum chamber 51 into a gas return line which is connected to a volatile recovery sys tern, 60, 61. Subsequent to removal of glycol and oligomers in condenser 60 and storage tank 61, the gas is returned to the gas recirculation system.
A level controller 50 is positioned near the top of tower 47 for controlling the residence time of the polymer within the tower. The discharge rotary valve 58 is actuated by the level control mechanism to release the material at the same rate of introduction. A receiver 51 is The polymer lots that were processed by solid-state polymerization in accordance with the present invention exhibited a significant drop in breaks and wraps when spun into fibers. Approximately 50 percent less breaks and wraps were encountered. The improved properties are beprovided to function as a surge means on the continuous lieved to be attributed to the removal of low molecular y f 111 cases of Product ug overs or equlpmentreweight material from the polyester. Therefore, the forepalr. The polymer, after having attalned the deslred going improvements make the products of this invention molecular weight and/or purity 1s forwarded to a blender particularly de irable for the production of fibers h re 55 where the pellets undergo a. thorough blending prior spin-draw te hni ue are used, to being forwarded to spinning y t s In Examples 7-10 the height and diameter of the crysa more e e dlsclosvre of the dry1ng app tallizer, in feet, was 33/3, 33/3, 40/4 and 40/4, respectivep y hereln Wlth regard to opefatlng eendltlons See 1y. At a hight of less than 5 times the diameter of the crystallizer column considerable bypassing occurs which The followleg examples further Illustrate the lllvelltlon then caused mechanical difliculties due to sticking of said In greater detail. bypassing, low-crystallinity polyester. Using an overflow EXAMPLES tube of less than 3 inches in diameter resulted in bridging In general, the molecular weight of polyester will inpluggase by the Polyester Peuets- The crease principally as a function of the drying temperature mg sohd'state polymeljllatlon column employed for employed, and the superficial velocity of the inert gas EXan}P1e$ had a helght and dlameter 111 feet, employed. This is shown in Table II, below, wherein Spectlvely: /5, 49/5, 72/10 and 2 Foridrymg Examples 1-6 demonstrate that an increase in molecular eolllmns havmg a helght less than 6 tlines the dlametel weight and increase i melting point i hi v d up t noticeable polyester nonuniformity could be detected in the 210 C. subsequent spinning and drawing opeartion because of the TABLE II Example No 1 2 3 4 5 1 6 1 6a Initial vise. OCP 0.6 0.8 1.0 0.8 0.6 0.8 0.6 Melting point, 0..... 2 58 262 258 254 25s 25s MoLWeight No., avg 28,100 22,160 14,254 22,160 14, 254 Temp .of inert gas passing through drying column,
0 0-- 160 180 190 200 210 220 200 Time in 1118., gas flow 24 12 8 6 6 4 10 0GP vise. alter solid-state polymerization 0.68 0. 88 1. 2 1. 0 0.75 0. 88 0. 6 Gas flow superficial velocity, ft/sec 1. 5 1. 5 l. 8 2. 0 2. 0 2. 0 0 MoLwt. after polymerization 17,800 25,000 32, 700 28,100 23,200 26,000 14,254 Mol. wt. increase per hour 4,300 2,300 4,6 6,000 8,950 3,800 0 Melt. point after stripping off impurities, C- 254 261 266 263 2 258 258 M01. wt. increase per hour 180 192 580 1, 000 1, 500 800 1 This example show ed an undersirable tendency to stick and there was no increase in melting point oi the resulting polymer. Therefore, it is assumed that some degradation occured.
i Heated with a jacket; no gas flow employed.
The molecular weight increase is illustrated graphically in FIG. 3 as a function of temperature by plotting the rate of molecular weight increase per hour against the temperature at a constant gas flow of 2.0 ft./sec. superrficial velocity. It will be noticed that the rate of increase is quite rapid for temperatures beginning at 180 C. and continues to increase until reaching 210 C. at which point the rate decreases rapidly. It may also be noticed that in the absence of sufficient inert gas flow or equivalent partial pressure reducing technique that essentially no rise in molecular weight occurs.
EXAMPLES 7-l0 In Table III below, there is shown detailed Examples 7-10 illustrating specific. conditions, properties and dimensions of apparatus which are employed for practicing the invention disclosed herein. The polymer employed in Examples 7-10 was polyethylene terephthalate.
TABLE III Example No 7 8 9 0 Pounds molten PET polymer feed/hour- 4, 000 4, 000 10, 000 10, 000 Viscosity 0 Cl? 0. 72 0. 72 0. 68 0. 75 Gas, c.i.m. 1, 400 1, 400 2,200 2,200 crystallizer temperature, C 180 180 178 178 .Avg. percent crystallinity/res. time in 80/4 80/4 60/3 60/3 minutes required to achieve crystallinity Drying temp. C 160 200 200 210 Drying time, hours. 4 8 6 8 Sohd-state polymer1zat1o No Yes Yes Yes DTA melting point before dry g, 260 260 260 258 DTA melting point after drying, C 260 264 264 261 OCP viscosity after drying 0. 72 0. 95 0. 86 1. 32 Molecular weight increase/hour; None 1, 000 1, 000 1, 500 No. average molecular weight at start- 21, 000 18, 000 18, 000 22, 000
No. average molecular weight at exit of drying tower 21, 000 26, 800 24, 000 34, 400
1 In Table III the residence time between the extrusion die and the crystallizer chamber for Examples 7-10 is 4, 4, 3, 3 seconds, respectively.
2 Gas superficial velocity-2.9 it/sec.
3 Good.
4 Very good.
greater incidence of breaks and wraps. This was due to nonuniform moisture and melt viscosity for polyester pellets bypassing within the column.
The cross-sectional area of the drying column employed was 2.8 times greater than the crystallizer column for Examples 7 and 8 and 6.3 times greater for Examples 9 and 10. For a crystallizer having a cross-sectional area of less than 2.0, the manufacturing costs and mechanical problems make these operations unsatisfactory.
Although several specific examples of the inventive concept have been described, the invention should not be construed as limited thereby nor to the specific features mentioned except as set forth in the appended claims.
What is claimed is:
1. In a process for crystallizing and drying linear, fiber forming crystallizable polyesters having a crystallization activation temperature at least 50 C. above its glass transition temperature wherein the polyester is extruded in a molten state through a die plate to form individual strands which are reduced to pellets, the improvement which com. prises surface quenching said extruded polyester strands at a temperature between 15 and 70 C. by contacting them with a liquid having a heat capacity of at least 0.6 caL/gram/ C. for a period not to exceed 3 seconds, pelletizing said surface quenched polyester strands to form pellets and maintaining the average temperature of said pellets above 130 C. until crystallization has been achieved, at least 60 percent crystallinity being attained within a period of 3 to 38 minutes.
2. The process of claim 1 in which at least 60 percent crystallinity of the pellets is attained within a period of 3 to 6.1 minutes.
4. The process of claim 3 in which the gaseous medium is heated to between 130 and 190 C.
5. The process of claim 4 in which the residence time of the pellets within the fluidization zone is from about 2 to 30 minutes whereupon at least 50 percent crystallinity is obtained.
6. The process of claim 5 in which the temperature of the gas entering the crystallizer is maintained between about 150 and 180 C.
7. The process of claim 6 in which the pellets are continuously transferred from the fluidization zone to a drying tower after crystallization has occurred.
8. The process of claim 7 in which the pellets are dried and simultaneously solid-state polymerized by passing an inert gas therethrough at a superficial velocity of 0.5 to 2.1 feet/sec. and heated at a temperature of 180 to 212 C. until an intrinsic viscosity of between 0.7 and 1.3 deciliters per gram is attained.
10 References Cited UNITED STATES PATENTS 2,850,764 9/ 1958 Evans et al. 18-1 2,901,466 8/1959 Kibler et a1 26075 5 2,975,483 3/1961 Cooper et a1 1847.5
3,075,952 1/ 1963 Coover et al. 26075 3,342,782 9/1967 Barkey 260-75 3,405,098 10/ 1968 Heighton et a1 260-75 10 FOREIGN PATENTS 1,066,162 4/ 1967 Great Britain.
WILLIAM H. SHORT, Primary Examiner 15 M. GOLDSTEIN, Assistant Examiner US. Cl. X.R.
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US716089A Expired - Lifetime US3544525A (en) | 1968-03-26 | 1968-03-26 | Process for crystallization,drying and solid-state polymerization of polyesters |
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US3949039A (en) * | 1972-04-03 | 1976-04-06 | Japan Steel Works, Ltd. | Method for pelletizing synthetic resins having a high melting point |
US3960817A (en) * | 1970-10-23 | 1976-06-01 | Ciba-Geigy Ag | Solid phase polyester polycondensation |
US3969324A (en) * | 1972-01-13 | 1976-07-13 | Monsanto Company | Continuous process for drying, crystallizing and solid state polymerizing polyesters |
US4064112A (en) * | 1975-12-31 | 1977-12-20 | Zimmer Aktiengesellschaft | Process for the continuous production of high molecular weight polyethylene terephthalate |
US4080317A (en) * | 1970-10-23 | 1978-03-21 | Ciba-Geigy Ag | High molecular weight polycondensates from solid phase condensation |
DE2919008A1 (en) * | 1978-05-16 | 1979-11-29 | Celanese Corp | PROCESS FOR THE MANUFACTURING OF POLYAETHYLENE TEREPHTHALATE WITH A REDUCED ACETALDEHYDE CONTENT |
US4231991A (en) * | 1976-09-18 | 1980-11-04 | Buehler-Miag Gmbh | Apparatus for crystallizing an amorphous particulate material |
US4258178A (en) * | 1978-12-01 | 1981-03-24 | Basf Aktiengesellschaft | Discharging granular linear polycondensates |
US4289871A (en) * | 1980-03-27 | 1981-09-15 | Allied Chemical Corporation | Method to increase reactor capacity for polycondensation of polyesters |
US4379912A (en) * | 1982-08-12 | 1983-04-12 | Eastman Kodak Company | Method of making polyester prepolymers |
US4446303A (en) * | 1983-07-26 | 1984-05-01 | Eastman Kodak Company | Process for preparing high molecular weight polyesters |
US4769200A (en) * | 1985-06-22 | 1988-09-06 | Basf Aktiengesellschaft | Compounding crystalline organic materials |
EP0379684A2 (en) * | 1988-12-23 | 1990-08-01 | Bühler Ag | Method of and apparatus for the continuous crystallisation of polyesters |
US5391355A (en) * | 1993-07-21 | 1995-02-21 | Eastman Chemical Company | Vessel for the treatment of particulate materials |
US5408035A (en) * | 1991-10-16 | 1995-04-18 | Shell Oil Company | Solid state polymerization |
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Also Published As
Publication number | Publication date |
---|---|
GB1257967A (en) | 1971-12-22 |
DE1905677A1 (en) | 1969-10-09 |
ES363300A1 (en) | 1970-12-16 |
FR2004707A1 (en) | 1969-11-28 |
BE727929A (en) | 1969-08-05 |
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